Separation of hydrocarbons with activated carbon

ABSTRACT

HYDROCARBON MIXTURES, SUCH AS LIGHT CYCLE OILS FROM A CATALYTIC CRACKING UNIT, PARAFFINIC LUBRICATING OILS AND THE LIKE, ARE SELECTIVELY SEPARATED BY A CYCLIC ADSORPTION TECHNIQUE INVOLVING PASSING THE HYDROCARBON MIXTURE THROUGH A FIXED BED OF ACTIVATED CARBON TO ADSORB SELECTIVELY MORE READILY ADSORBED COMPONENTS OR AN ADSORBATE PHASE WHILE COLLECTING LESS READILY ADSORBED COMPONENTS OR A RAFFINATE PHASE; PASSING A FIRST PORTION OF A PREDETERMINED VOLUME OF CARBON DISULFIDE THROUGH THE CARBON TO DISPLACE THE ADSORBATE PHASE WHILE COLLECTING A PORTION OF THE RAFFINATE PHASE AS A RECYCLE STREAM; PASSING THE REMAINDER OF THE CARBON DISULFIDE THROUGH THE CARBON WHILE COLLECTING AN ADSORBATE PHASE; PASSING A FIRST PORTION OF THE COLLECTED RECYCLE MATERIAL THROUGH THE CARBON WHILE COLLECTING AN ADSORBATE PHASE; PASSING THE REMAINDER OF THE COLLECTED RECYCLE MATERIAL THROUGH THE CARBON WHILE COLLECTING A RAFFINATE PHASE; AND SEPARATING CARBON DISULFIDE FROM THE RAFFINATE AND ADSORBATE PHASE FOR REUSE AS A DISPLACING FLUID.

Spt. 5, 1972 L. HQFER El AL SEPARATION OF HYDROCARBONS WITH ACTIVATED CARBON Filed April 5, 1971 2 Sheets-Sheet l 'T'ILLSIG TILLSIO HEIOSOV ATTORNEY Sept 5, 1972 J. HOFER ETAL 3,689,404

SEPARATION OF HYDROCARBONSWITH- ACTIVATED CARBON Filed April 5, 1971 Y 2 Sheets-Sheet 2 a o N E U 8 I [D Q.

I I O (D 8 '2 3 i i? INVENTORS XBCINI :muovauaa LAWRENCE J.E. HO R DAVID B. CARPENTER By EDWARD A.THOMPSON 51 ATTORNEY "United States Patent Office 3,689,404 Patented Sept. 5, 1972 US. Cl. 208-310 18 Claims ABSTRACT OF THE DISCLOSURE Hydrocarbon mixtures, such as light cycle oils from a catalytic cracking unit, parafiinic lubricating oils and the like, are selectively separated by a cyclic adsorption technique involving passing the hydrocarbon mixture through a fixed bed of activated carbon to adsorb selectively more readily adsorbed components or an adsorbate phase while collecting less readily adsorbed components or a rafiinate phase; passing a first portion of a predetermined volume of carbon disulfide through the carbon to displace the adsorbate phase while collecting a portion of the raffinate phase as a recycle stream; passing the remainder of the carbon disulfide through the carbon while collecting an adsorbate phase; passing a first portion of the collected recycle material through the carbon while collecting an adsorbate phase; passing the remainder of the collected recycle material through the carbon while collecting a raffinate phase; and separating carbon disulfide from the raffinate and adsorbate phase for reuse as a displacing fluid.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to the separation of hydrocarbon mixtures. More specifically, the present invention relates to the separation of aromatic hydrocarbons from mixtures of such aromatic hydrocarbons with aliphatic hydrocarbons. Still more specifically, the present inven tion relates to the separation of polycyclic aromatics from a light cycle oil of a catalytic cracking operation by contacting the cycle oil with activated carbon to selectively adsorb the polycyclic aromatics and thereafter displacing the polycyclic aromatics with carbon disulfide.

Description of the prior art Many refinery operations require the separation of various types of hydrocarbons from one another. In many cases, aromatic hydrocarbons, such as benzene, toluene, xylenes, naphthalenes and the like, must be recovered or separated from mixtures of the same with aliphatic hydrocarbons or from one another. Such separations are generally carried out for the purpose of producing chemical grade aromatics or for improving the quality of certain low grade hydrocarbon fractions.

One of the primary products sought to be recovered in refinery operations because of its commercial value is naphthalene. The chemical importance of naphthalene resides primarily in its use as an intermediate in the production of phthalic anhydride. For example, roughly 80% of all of the naphthalene produced domestically is consumed in the production of phthalic anhydride.

Heretofore, the primary source of naphthalene has been coal tar fractions. However, the uncertainties and fluctuations in the production of coal tars makes it undesirable to tie the production of naphthalene to such variable sources, particularly since the major portion of coal tar is produced as a by-product of the manufacture of coke for the production of steel.

Naphthalene does not exist in any great volumes in crude petroleum hydrocarbons. While the amounts of naphthalene in crude oils varies to some extent, the total of all aromatic hydrocarbons in petroleum is usually only about 5%. Accordingly, it is impractical to separate such naphthalene from the crude by simple distillation, since a number of other contaminating materials boil in the same boiling range. However, certain refined petroleum fractions, such as fractions obtained as products of catalytic reforming, catalytic cracking and thermal cracking, do contain significant quantities of naphthalene and alkyl-substituted naphthalenes to be of interest as feedstocks for further processing. Some feedstocks, and, particularly, products of catalytic cracking contain large quantities of naphthalene and alkyl-substituted naphthalenes and only minor quantities of monocyclic aromatic and paraifins. These feeds may, therefore, be directly processed to convert the alkyl naphthalenes to naphthalene. However, when attempting to process fractions containing smaller amounts of naphthalene precursors, it becomes impractical and prohibitively expensive, to convert this feed to naphthalene.

While a number of techniques for concentrating naphthalene precursors have been tested in the past, and found useful to a greater or lesser extent, few have been found to economically produce substantial quantities of naphthalene precursors which, in turn, produce economic yields of naphthalene. However, one effective technique has been the utilization of solvents for the separation of parafiins and monocyclic hydrocarbons from dicyclic or polycyclic hydrocarbons in the feed material. While such solvents are effective in varying degrees, the commercial use of such solvents has been practically nil. There are believed to be several basic reasons for such lack of utility and these are primarily directed to the amount of solvent required and hence the cost of operation. In addition, there is a limit to the degree of separation which can be practically and economically eflfected by the use of a solvent. Even after concentration of polycyclic hydrocarbons by the use of a solvent, there still remain paraflinic and monocyclic aromatic hydrocarbons which boil in substantially the same range as the polycyclic hydrocarbons of interest.

Another problem area in the processing of petroleum products is the treatment of wax distillates. Wax distillates are lubricating oil distillates from petroleum. Normally, these materials are dewaxed, earth treated and filtered to produce neutral lubricating oils and wax. However, due to the presence therein of aromatics, the products have a very poor viscosity index and a dark color, thereby making them undesirable for their intended purpose. At present, there is no satisfactory technique for removing the aromatics.

It is also known that numerous other petroleum or coal liquid streams could be greatly improved if there were some simple and economic manner of separating hydrocarbons by type and particularly separating aromatics from non-aromatics.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an improved method for the separation of hydrocarbons. Another and further object of the present invention is to provide an improved method for the separation of aromatic hydrocarbons from aliphatic hydrocarbons. Yet another object of the present invention is to provide an improved method for the separation of high concentrations of polycyclic hydrocarbons from hydrocarbon mixtures containing the same. Another object of the present invention is to provide an improved method for the production of polycyclic hydrocarbons from petroleum hydrocarbon mixtures. A still further object of the present invention is to provide an improved method for the production of polycyclic hydrocarbons from catalytic light cycle oils obtained from the catalytic cracking of petroleum hydrocarbons. Another and further object of the present invention is to provide an improved method for the production of polycyclic hydrocarbons by passing a petroleum hydrocarbon mixture containing parafiins, monocyclic aromatics, and dicyclic aromatics, through an adsorbent to separate dicyclic aromatics therefrom. A still further object of the present invention is to provide an improved method for the production of polycyclic hydrocarbons wherein a catalytic light cyclic oil is subjected to adsorption with an activated carbon, a raffinate phase is collected, adsorbate is displaced with carbon disulfide, the adsorbate phase is separated from the displacing fluid, and the displacing fiuid is recycled to the adsorption step. Another object of the present invention is to provide an improved method for the separation of dicyclic hydrocarbons from mixtures of dicyclic, monocyclic and parafiinic hydrocarbons. Another and further object of the present invention is to provide an improved method for the recovery of polycyclic aromatics from mixtures of polycyclic aromatics, monocyclic aromatics and paratfins wherein the mixture is subjected to contact with an activated carbon and the activated carbon is displaced with carbon disulfide. Yet another object of the present invention is to provide an improved process for improving the viscosity index of lubricating oils. Another and further object of the present invention is to provide an improved process for removing aromatic hydrocarbons from lubricating oils.

These and other objects and advantages of the present invention will be apparent from the following detailed description.

BRIEF DESCRIPTION OF THE INVENTION Briefly, in accordance with the present invention, hydrocarbon mixtures are separated into constituent groups, particularly into aromatic versus aliphatic hydrocarbons, polycyclic aromatics versus monocyclic aromatics and the like, by passing the mixture through activated carbon to produce an effluent rafiinate phase of the least readily adsorbed material and selectively adsorbing a more readily adsorbed material; passing carbon disulfide through the activated carbon containing the selectively adsorbed adsorbate to displace the same, and recovering the displaced adsorbate. Where the hydrocarbon mixture contains substantial volumes of polycyclic aromatics, the process is utilized to selectively adsorb such polycyclic aromatics.

The present invention will be more clearly understood by reference to the drawings when read in conjunction 'with the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS The details of the present invention Will be better understood by reference to the drawings, wherein:

FIG. 1 is a flow diagram illustrating the overall method of the present invention; and

FIG. 2 is a plot of refractive index versus time for a single cycle of operation in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION As will be illustrated by the following description, it has been found that the refractive index of the effluent from the adsorbtion column of the present invention or a time cycle may be effectively utilized to control the operation of the process of the present invention.

In accordance with FIG. 1 of the drawings, a liquid hydrocarbon feed material is introduced through line and valve 12 to fixed bed adsorption column 14 and thence upwardly through the column. Adsorption column 14 is, of course, filled wit-h a granular activated carbon which will selectively adsorb certain of the components of the feed material. The eflluent from column 14, comprising the non-adsorbed components (rafiinate phase), is discharged through line 16 and valve 18 to accumulator 20. There- 4 after, the feed to column 14 is switched from hydrocarbon feed material to carbon disulfide and a predetermined volume of carbon disulfide is passed through column 14. During the initial startup of the system, both the point of termination of hydrocarbon feed and the predetermined volume of carbon disulfide can be determined experimentally by observing a characteristic of the raifi nate phase and/or the adsorbate phase (preferentially adsorbed components), and adjusting the point of termination of the hydrocarbon feed and the volume of carbon disulfide until rafiinate and/ or adsorbate of the desired character is obtained. For example, the refractive indices of the raftinate and adsorbate phases may be observed, as will be more fully explained hereinafter. Once the point of termination of hydrocarbon feed and the volume of carbon disulfide have been established the system will have reached steady state conditions and the entire operation can be repeated on the cyclic operating basis hereinafter explained in detail. Sometime after introduction of carbon disulfide is begun, the raffinate efiluent will contain carbon disulfide. In order to separate the raftinate from the carbon disulfide, the effluent from accumulator 20 is passed through line 22 to distillation column 24. In distillation column 24 this mixture of raflinate and carbon disulfide is separated and the rafiinate is discharged through line 26 while the carbon disulfide is discharged through line 26, and, thence, through line 30 to accumulator 32. Carbon disulfide is fed from accumulator 32 through line 34 and valve 36 to the adsorption column 14. Where necessary, makeup carbon disulfide is introduced to ac cumulator 32 through line 38 and valve 40. The introduction of carbon disulfide to column 14 is carried out in two distinct phases. During the introduction of a first portion of carbon disulfide, raflinate discharged through line 26 of distillation column 24 is passed through line 42 and valve 44 to recycle accumulator 46. The amount of rafiinate collected at this point can also be determined by any convenient means. The portions of raffinate which are not collected in accumulator 46 may constitute the more desirable components of the feed material or the less desirable components of the feed material depending, of course, upon the nature of the feed material. For example, where a light cycle oil is to be separated, primarily for the recovery of dicycle hydrocarbons, the rafiinate phase will be the less desirable monocyclic and paraflinic materials. On the other hand, where a parafiinic lubricating oil is treated to improve its viscosity index, the ratfinate is the primary product. In any event, rafiinate which is not collected may be Withdrawn from distillation column 24 through line 48 and valve 50. The raflinate may be stored or otherwise utilized. After the first portion of carbon disulfide has been utilized, the second portion of a predetermined amount of carbon disulfide is passed through adsorption column 14. While the second portion of carbon disulfide is being passed through column 14, an adsorbed or adsorbate phase is passed through line 52 and valve 54 to adsorbate accumulator 56. This adsorbate stream comprises a mixture of the preferentially adsorbed components of the feed mixture and carbon disulfide. The adsorbate passes from accumulator 56 through line 58 to distillation column 60. In distillation column 60, the adsorbate is stripped of carbon disulfide and discharged through line 62 and valve 64 while the carbon disulfide is passed through line 64, and, thence, through line 30 to accumulator 32. After the predetermined volume of carbon disulfide has been utilized, the recycle raflinate collected in accumulator 46 is passed through line 66 and valve 68 as a recycle to adsorption colurrm 14. The intro duction of recycle to adsorption column 14 is also carried out in two separate phases. As a first portion of the recycle material is passed through adsorption column 14, the effluent from column 14 constitutes a further portion of the adsorbate phase which is collected and distilled as previously indicated. The end of the first recycle phase is determined in accordance with the previously mentioned criteria for controlling the operation. Thereafter, the second portion of recycle is passed through column 14 until all of the collected recycle has been used. During the introduction of this second portion of the recycle, the eflluent from the adsorption column is switched to the rafiinate handling portion of the system and thus is accumulated in accumulator 20 and distilled in distillation column 24. The rafiinate is then treated as previously described.

A suitable activated carbon for use in accordance with this present invention may have a broad range of particle sizes, for example 4 x 6 to 20 x 50 mesh size (U.S. sieve series). The following physical properties are also desirable:

Total Surface Area (N BET Method mF/g. 500-1500 Apparent density (bulk density, dense packg./cc. 0.3-0.6

lb./ft. 20-30 Particle Density (Hg displacement), g./cc. 0.5-1.0 Real density (He displacement), g./ cc 2.0-2.2 Pore volume (within particle), cc./ g 0.5-1.5 Voids in dense packed column, percent 20-50 Specific heat at 100 C. --M. 0.2-0.3

Brunauer, Emmett and Teller: J. Am. Chem. Soc. 60, 309 (1938).

The following examples illustrate the practice of the present invention and compare the same with similar techniques.

In all of the examples, the activated carbon utilized as an adsorbent is formed from bituminous coal combined with suitable binders and is activated with steam at a high temperature. The particle size is 12 x 40 mesh size (U.S. sieve series). This activated carbon had the following physical properties.

TABLE I Physical properties activated carbon Total surface area (N BET Method m. g 1000-1100 Apparent Density (bulk density, dense pack- Brunauer, Emmett and Teller: .1. Am. Chem. Soc. 60, 3 (1938). 09

Except where otherwise noted, the feed material employed was a 430 to 550 P. out of a light cycle oil from the catalytic cracking operation. Table II below lists the properties of a typical feed material of this type.

TABLE II Properties of Light Cycle Oil AS'IM distillation, F;

IBP

E API gravity at 60. Specific gravity 60/60- m3 Table III below summarizes four cycles of adsorptiondisplacement wherein a light cycle oil heart out was adsorbed on activated carbon and thereafter displaced by steam stripping at 600 F. It is to be observed that steam stripping is relatively ineffective. The capacity of the carbon decreases very sharply throughout the adsorptiondisplacement when utilizing steam as a recovery agent. In addition, when polycyclic aromatics are to be separated, the refractive index of the efiluent raffinate should be below about 1.5. In the run illustrated, the rafiinate refractive index was below that figure for only about 5 to 10 minutes and it rapidly increased to that of the feed material (about 1.5163) after only 18 to 20 minutes. The refractive index of the adsorbate is also too low since polycyclic concentrates should have a refractive index above about 1.54 and preferably near 1.6. Where the refractive index of a stream, such as raffinate or adsorbate, is referred to, this represents the refractive index of the particular steam after carbon disulfide has been removed therefrom.

Grams adsorbed (by diti.) Recovery, gms

Loss, gms"--. Adsorbate RI.

A second test was made with the same feed material, the same activated carbon, and in the same equipment but with carbon disulfide as the displacing agent. The results of this test are set forth in Table IV below. It is obvious from Table IV that the capacity of the carbon bed decreased over the first several cycles, but then remained substantially constant. Also, except for the first run when the carbon was dry, the time needed to reach an efiluent refractive index of 1.5 after collection of the first efiluent, was about 10 to 20 minutes. This is more than twice the length of time observed when steam stripping. This shows that the use of carbon disulfide as a displacing media not only provides high carbon capacity but it also gives a higher selectivity for the polycyclic hydrocarbons sought to be extracted from the light cycle oil. Thus, carbon disulfide displacement results in a higher overall carbon capacity and a higher yield of the polycyclic hydrocarbon materials. This higher yield of the polycyclic hydrocarbon materials is a function of the higher equilibrium capacity of the carbon, the ability of the carbon disulfide to effectively displace these polycyclic hydrocarbon materials, and the higher selectivity for polycyclic hydrocarbon materials which the carbon disulfide imparts to the carbon.

TABLE IV Carbon Dlsulfide Displacement Cycle 1 2 3 4 5 I 6 Charged Refractive Index 1.5160 1.5160 1. 5160 1. 5160 1.5160 1. 5160 Weight, gms 2, 252 2, 687 2, 651 2, 661 2, 678 2, 685

Pumped efliuent, gms 896 1, 213 1, 246 1, 286 1, 600 1, 281 Blowdown, gms 652 706 725 706 304 729 Total raifinate,

gms 1, 548 1, 919 1, 971 1, 992 1, 994 2,010

Adsorbate, gms 704 768 680 669 684 675 Recovery, gms- 641 700 724 664 669 643 Gain or loss, gms 63 -68 +44 +5 -15 -32 Vol. pumped in at 1st efiiluent, cc 1,435 960 990 870 820 825 Time to 1st efliuent,

min 62 37 40 39 38 35 The qual1ty of adsorbate from the two previous tests TABLE V1 is given below.

Phase In Out Valves open Termination of phase A Feed-. Raffinate 12, 18 and When R1 of rafilnate 082. 60. reaches 1.49. B CS2 Recycle--- 36 1 18 and When gtl tifsrsecycle I680 88 adsorbate quahty C CS2-.." Adsorbate 86, 54 and When all of predeter- (Table n (Table IV runs) CS2. 68 or 76. 111513531 volume of CS2 a g g Smpped adsorliai D Recycle "do 72,634 2%! When 11H tliifigdsorbate or reae es Gas ehromatogiaph Feed adsorbate Cycle 1 Cycle 2 Cycle 3 E 410"- Raflinate 72 18 and when an of collected BMN 51. o 47. o 40.9 41. 7 41. 7 recycle is used In the operation of the adsorption-displacement cycle,

A series of runs was made also in order to determine whether benzene could be utilized as a displacing medium. While benzene was found to be a fairly effective displacing medium, such displacement required volumetric ratios of benzene to light cycle oil feed of 10 to 1 or greater, in order to recover 95% or more of the light cycle oil hydrocarbons from the adsorbent. This becomes economically prohibitive.

Table V below summarizes an adsorption-displacement run in .which recycle of a selected portion of the efiluent material was practiced. It is to be noted from Table V that collection of recycle material was terminated during the cycle when the refractive index of the efiluent being collected for recycle material reached 1.52. As is pointed out hereinafter, this is an optimum cut point for the recycle operation when utilizing refractive index as a control and selectively adsorbing polycyclic hydrocarbons.

TABLE V Fresh feed, gms. 579 Fresh feed, ccs. 640 Recycle feed, gms 772 Recycle feed, ccs. 860 Raflinate:

Weight, gms. 199 Final RI 1.489 Average RI 1.476 Naphthalene precursors, percent 5.2 Yield, wt. percent 36.3 Recycle:

Weight, gms. 807 Volume, ccs. 900 Initial RI 1.489 Final RI 1.520 Average R1 1.512 Adsorbate:

Weight, gms. 349 Average RI 1.550 Naphthalene precursors, percent 51.3 Yield, wt. percent 63.7 Naphthalene precursors recovered, percent on feed 32.7 Cycle time, minutes 255 Adsorption rate, ccs./min. 11.5 Desorption rate, ccs./min. 23.0 Vol. CS ccs. 3000 No blowdown after adsorption Blowdown after desorption As a result of the conduct of operations utilizing a recycle phase and the conduct of tests while varying other conditions of operation, it was ultimately determined that the process of the present invention could most effectively be carried out by a cycle of operation involving adsorption and displacement in which five distinct phases were practiced. Table VI below illustrates the general character of this five-phase operation.

as illustrated in the Table VI above, the operation is broken down into five phases. It has been found in accordance with the present invention that switching of the input and output of adsorption column 14 from one phase to the next can be conveniently handled by monitoring the output stream and performing the switching operation at such times as certain refractive indices are measured. It has been found in accordance with the present invention that the refractive index of the efiluent is an excellent measure of how the adsorption column is operating and when each phase of the operation is essentially completed. The refractive index is, of course, an excellent indicator of the character of hydrocarbons since pure alkyl naphthalenes normally have a refractive index of about 1.6, monocyclic hydrocarbons have lower refractive indices and paraflinic hydrocarbons have still lower refractive indices.

Referring now to the above Table VI, it is to be seen that during Phase A of the operation, the light cycle oil feed is introduced to the system by opening valve 12 and the nonadsorbed rafiinate is passed through valves 18 and ultimately 50 for collection or further use. This phase of the operation is continued until the refractive index of the raflinate eflluent reaches a value of about 1.49. At this time, valve 36 is opened to introduce carbon disulfide to adsorption column 14 and Phase B of the operation is started. During Phase B of the operation, valves 18 and 44 are opened to collect recycle material in accumulator 46. Phase B of the operation continues until the refractive index of the recycle effluent stream being collected reaches a value of about 1.58. It is to be noted that the refractive index of the recycle is the primary control point. At this point, Phase C of the operation begins. During Phase C of the operation, valve 36 remains open and carbon disulfide continues to be passed through adsorption column 14. However, valve 54 is opened to discharge adsorbate to adsorbate accumulator 56-the rafiinate valve 18 being closed. After a predetermined volume of carbon disulfide displacing fluid has been utilized, Phase C of the operation is terminated and Phase D is begun by opening valve 72 to begin the passage of recycle fluid from accumulator 46 through adsorption column 14. At the same time, valve 54 remains open to discharge adsorbate to accumulator 56. The adsorbate ultimately passes through valves 68 or 76. When the refractive index of the adsorbate reaches a value of about 1.52, Phase D is terminated and Phase E begins. During Phase E of the operation, recycle is continued through valve 72 until all of the collected recycle efiiuent is used and valves 18 and 50 are opened to discharge a further portion of raflinate phase. When all of the collected recycle material has been passed through adsorption column 14, Phase E is terminated and the next cycle is begun by switching to a Phase A operation. The volumes of materials handled during a complete cycle and, of course, the sizing of the equipment utilized in the operation are, of course selected so that suflicient polycyclic aromatics are collected in accumulator 42 to continuously operate the remainder of the hydrogen treating and hydrodealkylating operations.

While specific refractive indices are given by way of example, the process can be varied depending upon the nature of the feed and the desired end product. Eflective results can be obtained by selecting refractive indices as follows:

End of Phase A 1.45-1.55 End of Phase B 1.47-1.59 End of Phase D 1.451.55

Table VII below summarizes an optimum treatment of light cycle oil feed when carried out in the five-phase cyclic manner set forth in Table VI.

TABLE VII Fresh feed, gms. 533 Fresh feed, ccs. 595 Recycle feed, gms. 854 Recycle feed, ccs. 950 Raflinate:

Weight, grns. 217

Final RI 1.495

Average RI 1.475 Recycle:

Weight, grns. 872

Volume, ccs. 980

Initial RI 1.495

Final RI 1.523

Average RI 1.523 Adsorbate:

Weight, gms. 304

Average RI 1.552

Naphthalene precursors, percent 56.1

Yield, wt. percent 58.3

Naphthalene precursors recovered, percent on feed 32.7

Cycle time, minutes 150 Adsorption rate, ccs./min. 23.0

Desorption rate, ccs./min. 23.0

CS vol., ccs. 2000 No blowdown after adsorption No blowdown after desorption The first column of Table VIII compares operation in accordance with the present invention when the activated carbon had been used for six cycles of adsorption-displacement with a similar operation as set forth in column two where the carbon had been used for seventy-nine cycles of adsorption-displacement. It is, of course, quite obvious from the data of Table VIII that no observable deactivation of the carbon takes place and it is just as eifective after the 79th cycle as it was after the 6th cycle.

TABLE VIII Fresh feed, gms 867 859 Fresh feed, cc 940 960 Recycle feed, gms- 420 460 Recycle feed, cc 470 505 Column length, it 8 8 Rafiinate:

Weight, gms- 173 186 Final RI 1. 402 1. 404 1. 467 1. 471 Recycle:

Weight, grns 426 256 Average RI 1 1. 515 l 1. 515 Adsorbate:

Weight, gms 652 662 Average RI 1. 533 1. 531 Naphthalene Precursors, percent. 43. 45. Yield, wt. percent 79. 0 78.1 Naphthalene precursors, percent on feed 34. 0 35. 5 CS; used, ce 3, 000 3, 000 Cycle time, min 370 212 Desorption rate, cc./mi 11. 5 22 Adsorption rate, cc./min 11. 5 22 1 Blowdown used.

Finally, Table IX of the examples shows the effectiveness of the process of the present invention on the removal of aromatics from a wax distillate of a low grade Pennsylvania crude oil. It is obvious from the data of Table IX that the adsorption technique is eifective in the removal of aromatics from the wax distillate. This is so since TABLE IX Adsorption of Wax Distillate Feed Efliuent Adsorbate Gravity, API 31. 4 34.9 11.9 Viscosity at 100 F., SUS 83. 15 79. 66 149. 8 Viscosity at 210 F., SUS 38.05 37. 67 40. 03 Viscosity index- 111 117 34 Pour point, I +75 +60 +50 Color 2- l). 5 7. 5

It is also quite obvious that other hydrocarbon materials may be separated in accordance with the present invention, including heavy oils, such as vacuum tower bottoms, etc. The only limitations on the type of material treated appear to be that there be no suspended solids in the liquid and the operating temperature should not be over 100 F., since such high temperatures cause the carbon disulfide to decompose. Hence, any material which is too viscous to pass through the column at temperatures below 100 F. should not be utilized in the process. However, such materials may be diluted with an appropriate solvent to permit handling in this process. Operation should not be conducted below 60 F. and preferably, not below 75 F. Column pressures of 15 to 35 p.s.i. are suitable.

As a general proposition, flow rates of feed, displacing fluid and recycle may vary anywhere between 0.05 gallon per minute per square foot of cross-section of the carbon column to as high as 10 gallons per minute per square foot. A preferred rate is 2.0 to 4.5 gallons per minute per square foot for feed and displacing fluid. Experimentation has shown that there is no real advantage in utilizing a column greater than about 10 feet in length. However, by doubling the length of the bed, the flow rate can be doubled and plant capacity increased accordingly. The recycle feed rate is preferably 3.5 to 5.0. The carbon disulfide-to-feed ratio may also vary considerably. This ratio should be at least 1 to 1 but may be anywhere above this limit. As the previous data has indicated, it is possible to recover a very pure methyl naphthalene fraction by increasing the amount of carbon disulfide employed. However, this increases the expense of removing carbon disulfide from the product. The use of high carbon disulfide ratios also requires increased capital investment due to the fact that the carbon disulfide is toxic and explosive.

Once a cycle of operation has been set up based on the refractive index cut point or some other measure of product quality, time-cycle control can be utilized to repeat the operation and predictably produce a product which meets the original specifications. Such time-cycle control has been utilized to produce a high-quality, polycyclic hydrocarbon material from the previously discussed light cycle oils. This desirable desorbate was produced at a nominal 4 gallons per minute per square foot feed rate and by initially utilizing a 1.58 refractive index cut point for the second phase of the recycle stream. When operating in this manner, the desorbate product has a refractive index of 1.59, contains to 88% polycyclic hydrocarbons and a 35% yield of desorbate is produced. Table X illustrates r-uns made in this tashion.

T ABLE X It is obvious from Table XII that the first portion of the recycle can be introduced in anywhere from 1450 to 1 2 3 4 5 1600, the second portion of recycle from 100 to 500 sec- Recycle feed, 01. lbs 120 104.5 104.5 102.5 100.0 onds, fresh feed from 500 to 900 seconds, the first portion Fresh feed wt-lbs 4 5 of carbon disulfide from 2000 to 2300 seconds, and the Total feed, wt. lbs 127 117.0 110.5 120.0 110.0 second portion of carbon disulfide from 500 to 1200 sesconds' and the total cyclic operation may vary from 52 15. 7 '8. 7 '03 10.0 9.1 to 5 800 seconds. This particular time cycle is for a column 1 23 3 S 1 23 3 1 1 8 1 235 having a height of 22 feet and a nominal diameter of 4 1 2 0001120; RL'IILIIII 1:4830 1.4865 114770 1: 4780 11 inches, or 0.088 square feet in cross sect1on, and utilizing a S 1 Bali. ercent 75.1 82.1 82.1 81.2 1 %,f, f, 1,200 1 50 1,000 1 050 1 050 4 gallon P?! mmute P q a foot fefed Obvlously Recycle, wt. lbs 100.5 108 105. 5 103.5 00.5 for other size columns, the time cycle will differ. However, out i r ti 1 222 102.98 the important point is that once a time cycle has been %l 1%%?:e0.-::. 2,300 2,800 2,000 2,300 2,800 established by utilizing product quality as a measure,

031M511 Period Sec-m whether this be by refractive index measurements or some Desorbate, wt lbs 3.3 4.2 4.3 4.2 4.8

Yield, per0ent 17.4 32.0 31. 28.4 34.5 other means, the time cycle can then be utihzed to carry Desorbate RI 1.5000 1. 5030 1.5040 1.5000 1.5800 out the operation and repeatedly produce products meet Naph.-ace. percent 88.02 86. 27 86.35 85.7 79.2 osiwt. percent desorbate. 00.0 00.1 00 00 05.5 mg the initial specifications. The cycle would, of course, change if a radical change in the composition of the feed Waive trouble. occurred. However, under normal operating conditions,

this will not be the case and the time cycle would nor- Table XI compares adsorption products having 80% mally be reset if a change in feed was made.

TABLE XII Time Cycle and Yields for Various Polycyclic Products Typical Typical Typical Typical 50% naph.-aoe. 60% mph-ace. 80% naph.-ace. 88% mph-ace.

Feed Efliuent Time Total Time Total Time Total Time Total Desorbate. 1, 000 1,000 1,500 1, 500 1, 450 1,450 1,450 1,450 Recycle "{Ratfmate 100 1,700 400 1, 000 550 2,000 500 1,950 Fresh feed Raifina 900 2, 600 800 2,700 500 2,500 500 2,4 0 2,000 4,000 2,100 4, 800 2, 300 4,800 2,300 4,750

Pounds of desorbate.-

Pounds oilinatphrace "d nd -1- 2 3 3- 8 3. 72

Carbone ec veness,p0un scar on pound of Hydeal teed 3 1 12. 6 12. 9

and 88%, respectively, of naphthalene-acenaphthene with the light cycle oil feed utilized in these runs.

TABLE XI Characterization of Products Pilot plant 80% 88% feed polycyelies polycyclics Gravity 21 11. 1 9.4

435 456 450 460 470 454 460 474 459 408 478 462 470 479 465 472 481 469 474 482 472 476 484 476 479 487 479 483 490 484 490 494 480 496 498 490 502 504 Chromatographs:

Naphthalene 62. 2 9. 10 4. 4 Naph.-ace 24. 2 82. 95 88. 14 Ace 13. 6 7. 95 7. 46

Table XII illustrates the effectiveness of time-cycle control in producing polycyclic products from a light cycle oil. By altering the time-cycle, products containing anywhere from 50% to 88% naphthalene-acenaphthene can be readily produced and of greater significance is the fact that a given product can be repeatedly produced from the same feed by utilizing the same time cycle.

Finally, Table XIII shows a comparison of a polycyclic product produced from light cycle oil in accordance with the present invention as compared with three commercially available materials which are sold for the Where the term more readily adsorbed components is used herein, it is meant to refer to the component or components of a multi-component mixture which the carbon will preferentially adsorb from the mixture to the exclusion of the less readily adsorbed components which will pass through the carbon without being adsorbed to any great extent. For example, the following order of adsorptive preference is recognized in the art for carbon, polycyclics monocyclics linear hydrocarbons, having refractive indices of greater than about 1.550, between about 1.550 and 1.480, and less than 1.480, respectively.

We claim:

1. A method for separatnig hydrocarbon mixtures; comprising, contacting said hydrocarbon mixture with activated carbon to selectively adsorb on said carbon 2 more readily adsorbed fraction of said hydrocarbon mixture and leave unadsorbed a less readily adsorbed fraction of said hydrocarbon mixture, and removing said selectively adsorbed hydrocarbon fraction from said carbon by pass ing carbon disulfide into said carbon.

2. A method in accordance with claim 1 wherein the hydrocarbon mixture contains cyclic and non-cyclic hydrocarbons and said cyclic hydrocarbons are selectively adsorbed.

3. A method in accordance with claim 1 wherein the hydrocarbon mixture contains polycyclic aromatic hydrocarbons, monocyclic aromatic hydrocarbons and aliphatic hydrocarbons and said polycyclic aromatic hydrocarbons are selectively adsorbed.

4. A method in accordance with claim 3 wherein the hydrocarbon mixture is a light cycle oil obtained from a catalytic cracking operation.

5. A method in accordance with claim 1 wherein a preselected portion of the effluent from the adsorptiondisplacement operation is recycled to the adsorption column.

6. A method in accordance with claim 1 wherein a predetermined volume of carbon disulfide is utilized as a displacing fluid.

7. A method in accordance with claim 1 wherein the adsorption-displacement is carried out utilizing a multiphase cyclic operation of a fixed bed of carbon.

8. A method in accordance with claim 7 wherein the cyclic operation is controlled by observing the refractive index of at least one predetermined stream and adjusting the operation as needed.

9. A method in accordance with claim 8 wherein the cyclic operation comprises passing the hydrocarbon mixture through the carbon and discharging an effluent comprising rafiinate and carbon disulfide; passing a first portion of carbon disulfide through said carbon and collecting an efiluent comprising a recycle mixture; passing a second portion of carbon disulfide through said carbon and collecting an effiuent comprising adsorbate and carbon disulfide; passing a first portion of said recycle mixture through said carbon while continuing to collect an efliuent comprising adsorbate and carbon disulfide, and passing the remaining portion of said recycle mixture through said column and collecting an additional portion of efiluent comprising raflinate and carbon disulfide.

10. A method in accordance with claim 9 wherein the hydrocarbon mixture is passed through the bed of carbon until the rafiinate has a first, predetermined refractive index.

11. A method in accordance with claim 9 wherein the first portion of carbon disulfide is passed through the carbon until the recycle has a second, predetermined refractive index higher than the first refractive index.

12. A method in accordance with claim 9 wherein 15. A method in accordance with claim 8 wherein the cyclic operation is controlled by utilizing a predetermined time of operation for each phase.

16. A method in accordance with claim 15 wherein the predetermined times are established by observing the refractive index of at least one predetermined stream, simultaneously measuring the time of operation for each phase and selecting the times at which the refractive index is a predetermined value.

17. A method of separating a mixture of cyclic and non-cyclic hydrocarbons comprising passing said mixture into and through activated carbon to adsorb thereon a mainly cyclic fraction of said mixture having a refractive index of at least about 1.45 and leaving unadsorbed a mainly non-cyclic fraction of said mixture having a refractive index of no greater than about 1.45, and removing the adsorbed fraction by passing carbon disulfide into and through the activated carbon.

18. A method in accordance with claim 17 including recycling a first portion of the adsorbed fraction, said first portion having a refractive index of no greater than about 1.59.

References Cited UNITED STATES PATENTS 2,395,491 2/1946 Mavity 260-674 SA 2,628,933 2/ 1953 Eagle et al. 260674 SA 2,848,379 8/1958 Rehner et al. 260-674 SA 2,756,197 7/1956 Thorpe et al. 260674 SA 3,340,316 9/1967 Wackher et al. 260-674 SA HERBERT LEVINE, Primary Examiner US. Cl. X.R.

260-666 SA, 674 SA, 674 N, 708 

